This invention relates to a method for forming carbon nanotubes and an apparatus for performing the inventive method.
Carbon nanotubes are tubules of carbon generally having a length of from 5 to 100 micrometers and a diameter of from 5 to 100 nanometers. Carbon nanotubes are formed from a plurality of co-axial cylinders of graphite sheets and have recently received a great deal of attention for use in different utilities such as fuel cells, fuel emission devices, catalysts, filtration and purification, sensors and microelectro mechanical manufacturing systems (MEMS) technology. Carbon nanotubes have many desirable properties such as a high strength and low weight compared with volume, energy and fuel storage capability, electron emission capability and many advantageous thermal, chemical and surface properties.
A particularly interesting property of carbon nanotubes is that their widths are just large enough to accept hydrogen molecules but too small for larger molecules. As a result, carbon nanotubes have drawn a great deal of attention as storage vehicles for hydrogen and, consequently, for use in fuel cell applications. Although carbon nanotubes have many advantageous properties, successful commercial application of them have not yet been reported due to the difficulty in synthesis capacity, manipulation and structural controllability of the carbon nanotubes. Therefore, there is a need for a method and apparatus which enables the synthesis of uniform carbon nanotubes in a cost effective and easily controllable method.
The present invention provides a method and apparatus for forming densely packed carbon nanotubes by a batch process. The carbon nanotubes can be formed in a high-density, close-packed configuration to enable large-scale production.
The present invention meets the needs outlined above by providing a method and apparatus for forming densified carbon nanotubes in which a chemical vapor deposition chamber having a coiled filament disposed therein is provided, a substrate having a catalytic coating provided thereon is supported inside the coiled filament, air is evacuated, if present, from the chamber, the filament is heated and a bias voltage applied between it and the substrate, a reactant gas is introduced into the chamber and the reactant gas is pyrolyzed to deposit carbon nanotubes on the substrate. When a cylindrical substrate is utilized, the carbon nanotubes can be aligned perpendicular to the longitudinal axis of the substrate and the radial growth of the carbon nanotubes allows for the formation of a densely packed configuration of the carbon nanotubes.